Over-expression of transcriptional activator/repressor gis1 in yeast for increased ethanol production

Abstract

Described are compositions and methods relating to modified yeast cells that over-expresses the transcriptional activator/repressor, GIS1. The yeast cells produce an increased amount of ethanol compared to their parental cells. Such yeast is particularly useful for large-scale ethanol production from starch substrates where increased ethanol production is desirable

What is claimed is: 
     
         1 . Modified yeast cells derived from parental yeast cells, the modified cells comprising a genetic alteration that causes the modified cells to produce an increased amount of GIS1 polypeptides compared to the parental cells, wherein the modified cells produce during fermentation an increased amount of alcohol compared to the amount of alcohol produced by the parental cells under identical fermentation conditions. 
     
     
         2 . The modified cells of  claim 1 , wherein the genetic alteration comprises the introduction into the parental cells of a nucleic acid capable of directing the expression of a GIS1 polypeptide to a level above that of the parental cell grown under equivalent conditions. 
     
     
         3 . The modified cells of  claim 1 , wherein the genetic alteration comprises the introduction of an expression cassette for expressing a GIS1 polypeptide. 
     
     
         4 . The modified cells of  claim 1 , wherein the genetic alteration comprises the introduction of an exogenous YDR096W gene. 
     
     
         5 . The modified cells of  claim 2 , wherein the genetic alteration comprises the introduction of a stronger promoter in an endogenous YDR096W gene. 
     
     
         6 . The modified cells of any of  claims 1 - 5 , wherein the amount of increase in the expression of the GIS1 polypeptide is at least about 10-fold compared to the level expression in the parental cells grown under equivalent conditions. 
     
     
         7 . The modified cells of any of  claims 1 - 5 , wherein the amount of increase in the production of mRNA encoding the GIS1 polypeptide is at least about 10-fold compared to the level in the parental cells grown under equivalent conditions. 
     
     
         8 . The modified cells of any of  claims 1 - 7 , wherein the cells further comprise an exogenous gene encoding a carbohydrate processing enzyme. 
     
     
         9 . The modified cells of any of  claims 1 - 8 , further comprising an alteration in the glycerol pathway and/or the acetyl-CoA pathway. 
     
     
         10 . The modified cells of any of  claims 1 - 9 , further comprising an alternative pathway for making ethanol. 
     
     
         11 . The modified cells of any of  claims 1 - 10 , wherein the cells are of a  Saccharomyces  spp. 
     
     
         12 . A method for increasing the production of ethanol in yeast cells grown on a carbohydrate substrate, comprising: introducing into parental yeast cells a genetic alteration that causes the modified cells to produce an increased amount of GIS1 polypeptides compared to the parental cells, wherein the modified cells produce an increased amount of ethanol compared to otherwise identical parental cells under equivalent fermentation conditions. 
     
     
         13 . The method of  claim 12 , wherein the genetic alteration comprises introduction into the parental cells of a nucleic acid capable of directing the expression of GIS1 to a level greater that of the parental cell grown under equivalent conditions. 
     
     
         14 . The method of  claim 12 , wherein the genetic alteration comprises introduction of an expression cassette for expressing GIS1. 
     
     
         15 . The method of any of  claims 12 - 14 , wherein the cells further comprise one or more genes of the phosphoketolase pathway. 
     
     
         16 . The method of  claim 15 , wherein the genes of the phosphoketolase pathway are selected from the group consisting of phosphoketolase, phosphotransacetylase and acetylating acetyl dehydrogenase. 
     
     
         17 . The method of any of  claims 12 - 16 , wherein the amount of increase in the expression of GIS1 is at least 10-fold higher compared to the level of expression in parental cells grown under equivalent conditions, based on GIS1-encoding mRNA expression. 
     
     
         18 . The method of any of any of  claims 12 - 17 , wherein the cells further comprise an exogenous gene encoding a carbohydrate processing enzyme. 
     
     
         19 . The method of any of  claims 12 - 18 , wherein the cells further comprise an alteration in the glycerol pathway and/or the acetyl-CoA pathway. 
     
     
         20 . The method of any of the  claims 12 - 19 , wherein the cells further comprise an alternative pathway for making ethanol. 
     
     
         21 . The method of any of  claims 12 - 20 , wherein the cells are of a  Saccharomyces  spp.